This invention relates to rolling bearings for hard disk drives (hereinafter referred to simply as HDD), in particular, rolling bearings appropriately employed in HDD components with rocking motion such as actuators (in particular, swing arms) or high-speed rotary motion such as spindles.
The present application is based on Japanese Patent Application No. Hei. 9-149403, which is incorporated herein by reference.
Although the computer industry has a short history compared with other industries, rapid technical innovation has been progressing in this field. Among all, HDDs undergo quick model changes and there have been developed novel ones for saving electricity, establishing quick response and high accuracy, downsizing, etc.
Under these circumstances, it has been required to improve the properties of bearings to be integrated into HDDs and prolonging the life thereof. For example, rolling bearings to be used in components with reciprocating rocking motion (for example, swing arm) should be highly resistant to fretting wear and have low torque and long life. Similarly, rolling bearings to be used in components with high-speed rotary motion (for example, spindle) should be excellent in heat resistance and high-speed rotary performance and have long life.
In a rolling bearing to be put into a swing arm, a spindle, etc. as shown in FIG. 1, for example, an inner ring 2 having the inner raceway surface 1 in its outer periphery and an outer ring 4 having the outer raceway surface 3 in its inner periphery are located concentrically and a plural number of balls 5,5 as rolling elements provided between the inner raceway surface 1 of the inner ring and the outer raceway surface 3 of the outer ring are supported by a cage 7 in such a manner as to allow free rolling. Circular sealing members 6,6 fixed to the both ends in the axial direction of the outer ring 4 prevent a grease lubricating oil (not shown in the figure), which has been injected into the bearing surface formed between the sealing members 6,6 from leakage. These sealing members also prevent the invasion of dusts suspending outside.
Although the grease lubrication is mainly employed for lubricating bearings, a rust proof lubricating oil is applied to the bearing raceway surfaces 1, 3, etc. prior to the injection of a grease in some cases. In the latter lubricating method, the initial lubrication is carried out by using not the grease but the lubricating oil so as to improve the lubricating performance.
Rotation is repeated at a minor rocking angle (usually 26° or below) in a swing arm rolling bearing. In the lubricating method with the use of a grease as described above, however, it is frequently observed that the lubricant masses are scraped out from the contact face, and also there is a possibility that the lubricant masses cause insufficient lubrication locally. This local insufficient lubrication induces fretting wear, thus shortening the life of the bearing. Moreover, the running torque at a minor angle is increased by the stirring resistance of the grease or the hang-up of the grease changes the torque. These phenomena lower the reliability of the HDD in reading and writing at high accuracy.
In a spindle bearing, use of a grease results in similar troubles such as an increase in running torque and changes in torque. In particular, the high-speed rotary performance is seriously affected thereby.
To solve these problems, attempts have been made to prevent the increase in torque and relieve the change therein by reducing the amount of the grease to be injected. When the grease is used only in an insufficient amount, however, there is a possibility that a fretting wear is arisen and the lubricating effect disappears earlier, which are not favorable from the viewpoint of the bearing life.
When the grease is injected in an increased amount, on the other hand, the increase and change in torque can be hardly regulated, though the fretting wear can be prevented and the bearing life can be prolonged thereby.
In the method wherein a rust proof lubricating oil is used together with a grease, the lubricating properties at the early stage can be particularly improved. However, this method essentially comprises injecting the grease. Therefore, the problems in association with grease cannot be fundamentally solved thereby.
In addition, it has been a practice to apply a rust proof lubricating oil onto a bearing by immersing the bearing in the rust proof lubricating oil. As a result, a large amount of the rust proof lubricating oil adheres to the outer periphery of the bearing, which does not directly participate in the lubricating effect, and makes it sticky and tacky. Before introducing into a HDD component (for example, swing arm unit or spindle motor), such a bearing should be cleansed by wiping, which brings about a decrease in the productivity and an increase in the production cost. Moreover, it is feared that the remaining lubricating oil might volatilize and stain recording media in the HDD.
As described above, there have been desired rolling bearings, which are components of HDDs aiming at saving electricity, establishing quick response and high accuracy, downsizing, etc., having high resistance to fretting wear, low torque, relieved torque change and long life. However, these requirements cannot be satisfied by using the existing grease lubricating method or the one with the combined use of a grease with a rust proof lubricating oil.